Infertility occurs in all herds but reproductive problems may become more
obvious with artificial insemination since mating related events are recorded
and summarized. Animal attendants often blame breeding failures on reproductive
abnormalities such as acyclicity, silent estrus, follicular defects or
insemination deficiencies. However, the inability to detect estrus so that
females can be mated at the opportune time is, although often overlooked, the
most frequent cause whenever artificial insemination is the principal mating
procedure. Those people responsible for executing insemination procedures need
a comprehensive understanding of reproductive function and sexual behavior to
appreciate how important their estrous detection activities are in contributing
toward the success of the entire program.

Estrous Cycles and Associated Sexual Behavior in Farm Mammals.

By the time of birth, female domesticated mammals possess a full complement
of oocytes (eggs) contained with primordial or primary follicles located at the
surface of their ovaries. No externally detectable evidence of ovarian activity
appears through the initial growing period until the animal reaches sufficient
physical size to undergo successful conception and gestation. At this time,
synchronization of the appropriate gonadotropin controlling hormones from the
anterior pituitary gland, plus the local regulatory mechanisms within the
ovary, allow complete follicular maturation and ovulation. Thereafter,
successive small groups of selected follicles commence final growth and
development toward maturity so the associated estrous cycles commence. Female
domesticated animals are anything but promiscuous, displaying only isolated and
usually short periods of sexual activity (estrus or heat) coinciding with final
follicular maturation. Estrogen, secreted by specialized endocrine cells
located in tissues forming the walls of growing follicles, stimulates both the
physical and behavioral signs of estrus. Thus, under natural conditions,
females only become sexually motivated and receptive near the time when
ovulation is imminent and conception is possible. Healthy, nonpregnant dairy
cows and sexually mature heifers are polyestrus, showing regular periods of
estrus throughout the year, unless pregnancy or pathology suppresses follicular
development and ovulation, thereby suspending the cycle. Estrogen injections
can produce estrous-like signs without follicular maturation and ovulation in
both intact cycling, pregnant and even ovariectomized females. Unfortunately,
veterinarians or herdspersons sometimes overlook this side effect accompanying
the therapeutic use of estrogen.

The bovine estrous cycle usually covers 17 to 23 days so normal, nonpregnant
cows should show signs of estrous behavior (heat) every three weeks.

The most infallible sign of estrus is a female's willingness to stand
immobilized and allow copulation to take place (a heterosexual interaction) or,
in the case of cattle and occasionally in other species, to accept mounting by
another female (a homosexual interaction). Many older references claim that the
bovine estrous period lasts for 18 hours or more but somewhat more recent
evidence indicates that it is considerably shorter for confined dairy cows
(Hurnik, King & Robertson, 1975, App. Anim. Ethol. 2:55). The occurrence of
short estrous periods in high producing dairy cows has been confirmed by a
number of subsequent research investigations conducted in both temperate and
tropical regions. Although considerable information on the relatively short
duration of estrus now exists in scientific journals, it has not yet been
widely incorporated into textbooks or extension publications.

A number of physical and behavioral signs may indicate that a cow or
heifer is in or near estrus. Some of the things to watch for are:

The best indicator of estrus is when any cow or heifer repeatedly stands and
accepts mounting by one of her herdmates. Unfortunately, they do not do this on
demand. Those responsible for estrous detection must watch for any of the above
indicators and, combining what they see with their own previous knowledge and
experience, make decisions on whether to inseminate or not.

What Do We Know About Getting Cows Mated at the Correct Time?

Whenever cows and bulls graze together on pasture or range, they interact
freely so that females in estrus rarely experience difficulty in locating
sexual partners and mating near the time of ovulation. Confinement housing,
however, places restrictions on normal reproductive behavior and patterns since
animals cannot mix continuously with members of the opposite sex. Under these
conditions the animal attendants must determine if and when service is given.
Selection of the appropriate time for mating would not seem to present a
problem since textbook descriptions of estrous behavior in cattle usually cite
the classical references of Hammond (1927) or Trimberger (1948) who each give
an average duration of 18 hours for temperate breeds.

In contrast to these older reports, a number of more recent investigations
indicate that the period of sexual receptivity and related behavior
demonstrated by confined Bos taurus dairy cows is considerably shorter than 18
hours (Table 1). Thus, a substantial number of females may pass through a
follicular phase and ovulate without being detected, so matings are not
performed at all (Williamson et al., 1972; King et al. 1976).

Table 1. Duration of Standing Estrus (hours) Demonstrated by Bos taurus
Dairy Cows Recorded From Continuous or Frequent Observations and Including
Substantial Numbers of Cycles.

Location

Breed

Mean ± SE

Remarks

Reference

USA

Various

11.9 ± 6.1

Winter & spring

Hall et al, 1959

Costa Rica

Jersey

10.5 ± 3.2

AI & natural mating

De Alba et al, 1961

Canada

Holstein

7.5 ± 2.4

10.1 ± 2.4

One in estrus
Three in estrus

Hurnik et al, 1975

Israel

Fresian

9.2 ± 0.4

10.6 ±; 0.4

Primiparous
Multiparous

Folman et al, 1979

England

Fresian

10.2 ± 1.2

Heifers

Esselmont et al, 1980

Thailand

Holstein

5.6 ± 1.1

5.1 ± 1.1

Cooler season
Hotter season

Pranee et al, 1996

Ovarian activity with follicular development, maturation and ovulation
occurs within a few weeks after calving in adequately fed, healthy cows even
under total confinement conditions. Unfortunately, the period when estrous
signs appear is short and many mounting-mounted interactions occur at night
when no one is present. Provided that ovarian activity commences early in the
postpartum period, failure to detect the first or second ovulation doesn't
depress performance since these should occur earlier than the dairyman normally
wish to rebreed. However, the third ovulation generally occurs around 60 days
and cows should be serviced by that time. In one study, conducted at the
University of Guelph with ovarian activity monitored by sequential measurement
of plasma progesterone concentrations and sexual behavior recorded with
tme-lapse videotaping, animal attendants were detecting only 64% of the normal
cycling cows at the third ovulation. Thus, one-third of the cows with normal
estrous periods and ovulations were missed. This resulted in delayed rebreeding
for a substantial number of animals and, even if conception occurred at the
first insemination, prolonged intercalving intervals. Although the barn staff
was certain that the cows were not functioning properly, the results indicated
that failure to rebreed at the desired time usually resulted from inability of
the herdsperson to detect estrus rather than because cows failed to cycle or
had silent heats (King et al. 1976).

As illustrated in Table 2, however, cows were in estrus for short periods
and had few mounting-mounted interactions unless other females were in or very
near estrus at the same time

Most of the 72 cows observed in the University of Guelph dairy herd for
collection of data presented in the above table had normal ovarian cycles
established soon after parturition and ovulated regularly throughout the year.
Acyclicity or ovulation without any detectable estrous signs were rare in this
situation. The postpartum ovarian activity and results should be similar
in healthy, adequately fed dairy cows under almost all conditions.

Some years later a similar study was conducted to determine seasonal effects
on postpartum ovarian activity, duration and intensity of sexual behavior for
Holstein dairy cattle imported from Canada (a temperate climate) into northern
Thailand (a tropical region). Animals, observed continuously during the cooler
and hotter seasons for each of two years, were restricted to cement footing in
an open-sided, pole-barn during the
hotter season observation period in year one. The cows had access to both
concrete and dirt footing during all other sessions in which they were under
continuous observation. Sequential milk progesterone profiled provided an
indication of when follicular phases occurred and recorded sexual behavior was
compared with these to determine if estrous signs accompanied ovulations.

A number of females showed sexually associated behavior patterns such as
sniffing and licking others during the hotter season observation periods. This
pattern suggested that they were coming into estrus but the suspect cows never
demonstrated any mounting-mounted behavior (Table 3). Although not conclusively
proven, it appeared that herdmates who were not in or near estrus were
sometimes reluctant to participate in homosexual interactions.

Table 3. Number of Ovulations and Detected Estrus Periods for Holstein Cows
Under Continuous Observation in a Tropical Environment.

Cooler Season

Hotter Season

Total cows

76

63

Cycling cows

73

61

Total ovulations in observation
period

130

126

Ovulations with detectable estrous
signs

118

93

Quiet ovulations, %

9

26

From Pranee, King, Subrod & Pongpiachan, 1996.

Constant observation of totally confined Holstein cows in a temperate
climate showed that once cows established regular ovarian cycles after
parturition, almost all ovulations were accompanied by some signs of estrus
behavior (King et al. 1976). The general results obtained in Thailand during
the cooler months were similar to findings in the Canadian study, but more
ovulations without detectable estrous signs were recorded in the hotter months
(Pranee et al, 1996). As stated above, one subjective impression formed
during the Thai study was that females in estrus may have been willing to
engage in homosexual interactions during the warmer season but their nonestrus
herdmates were less inclined. This reluctance to participate in mounting
activity would be even greater whenever animals were confined on slats,
concrete or any other slippery surface.

Thatcher and Collier (1982) found an even more disturbing pattern occurring
in Florida where half to two-thirds of potential estrous periods were missed in
cooler months but this increased to over 75% in late spring and summer.
Similarly, progesterone profiles compiled from Jersey and Holstein cows during
the hotter months in Pakistan showed that all cows were cycling regularly
(Imtiaz Hussain et al. 1992). However, with checking for estrus at 8 hours
intervals, behavioral signs were observed in conjunction with only 36% of the
ovulations. Although continuous observation can detect estrous signs for most
ovulating cows under research station conditions, this surveillance intensity
cannot be provided on commercial farms so the field situation is much closer to
that described by Thatcher and Collier (1982) or Imtiaz Hussain et al. (1992).
Farm operators must do whatever is practical to achieve reasonable detection
efficiency, recognizing that some animals will always be missed (King, 1993).
Whenever cows experience prolonged distress from any cause or animal attendants
are distracted by other seasonal duties, the incidence of missed estrous
periods will increase.

For those animals in Thailand that did engage in mounting-mounted
interactions, the actual demonstration of sexual behavior was affected more by
footing than by season. Cows that could move freely between the cement floored
shed and dirt exercise yard showed mounting-mounted interactions for 11.5
± 1.4 h in the cooler and 10.6 ± 1 h in the hotter seasons (Table 4).
In contrast, animals confined to the shed only during the one hotter season
showed sexual behavior for only 7.1 ± 1.4 h. Similarly, the actual time
when cows stood passively and allowed herdmates to mount and the mean number of
mounting-mounted interactions was significantly reduced during the observation
period when females were restricted to the cement flooring (Table 4).

Table 4. Intensity and Duration of Estrus Demonstrated by Holstein Cows in
a Tropical Environment.

Footing

Cement & dirt

Cement & dirt

Cement only

Season

Cooler

Hotter

Hotter

Mounting-mounted interactions,
No.

24.1 ± 4.2a

26.5 ± 2.6a

11.4 ± 3.8b

Total duration of mounting-mounted,
h

11.5 ± 1.4a

10.6 ± 1.0a

7.1 ± 1.4b

Total standing estrus, h

5.6 ± 1.1a

5.1 ± 1.1a

1.3 ± 1.1b

Row means with same superscript not significantly different
(P < 0.05).

These results certainly confirm the observations of Britt and coworkers
(1986) who found that for dairy animals in North Carolina, season of the year
had little influence on the duration or intensity of estrus. In contrast, the
surface on which cows were confined (cement vs. dirt) had a profound
effect on sexual behavior. The absence of a seasonal effect in North Carolina
and Thailand does not support the observations from Florida which suggest that
thermal stress alone produces a substantial reduction in the duration of estrus
(Gangwar et al., 1965; Thatcher and Collier, 1982).

Hall et al. (1959) reported the average duration of estrus was 11.9 ±
6.1 h with a range between 2 and 46 hours for dairy cows maintained primarily
on pasture in Louisiana. Although this study, conducted during the winter and
spring seasons in a subtropical region, is sometimes cited as an indication
that heat stress reduces the duration and intensity of estrus, the authors
actually state: "Thus, it appears that the explanation for shorter estrous
periods in this region is a complicated one, involving the possible interaction
of nutrition, parasites, climate and endocrine gland performances in the
cow." This extensive fertility study included many cows observed at
reasonably frequent intervals so the findings clearly indicate that estrus
duration for cows on pasture can be substantially shorter than the time periods
previously reported by Hammond (1927) and Trimberger (1948). Similarly,
continuous observation of Holstein cows, housed under total confinement in a
temperate climate, indicated that standing estrus lasted only 7.5 ± 2.4 h
and the total duration of mounting-mounted interactions rarely exceeded twelve
hours unless two or more animals were in or near estrus at the same time (Table
2; Hurnik et al., 1975). The times for duration of sexual behavior reported by
Hall et al. (1959) for dairy cows on pasture in a subtropical climate and by
Hurnik et al. (1975) for lactating cows under total confinement in a temperate
climate (Table 2) are similar to those found in Thailand whenever cows had
access to exercise yards (Pranee et al., 1996).

The research findings described above and summarized in Table 1 indicate
that many dairy animals in tropical and temperate regions show the classical
signs of estrous behavior for less than 12 hours throughout the year.
Collectively these reports certainly emphasize that the duration of estrus in
confined dairy cows is almost always considerably shorter than the commonly
quoted 18 hour period. It is likely that behavioral changes such as the shorter
and less intense periods of sexual behavior demonstrated by dairy cows under
various forms of stress, including total confinement, high production or
adverse conditions of any type, are adaptive mechanisms to intensive
management. Lindsay (1996), in his discussion of environmental effects on
reproductive behavior, pointed out that one of the greatest challenges facing
modern animal husbandry is to understand how the animal's surroundings
influence behavioral patterns and to match genotypes to conditions that enhance
productivity. Until such detailed knowledge and adapted genotypes are
available, dairy farmers must do the best they can with conventional resources.

Problem Solving

Reproductive problems occur in herds of all sizes but practical solutions
may differ between larger and smaller units. A logical beginning for any
program attempting to improve reproductive efficiency should be an holistic
assessment of the animals' environment to determine the physical and biological
factors that may be depressing or enhancing current performance. This should be
combined with a comprehensive analysis of breeding records to summarize past
competence. In addition, the necessary clinical examinations and laboratory
tests must be performed. With this information available, informed decisions
can then be made regarding the major defficiencies and the best options for
improvement. In most instances modifications will be needed so existing labor,
genetics, feeding, housing, health and breeding practices must be examined in
detail to identify major constraints and to devise practical solutions.
Informed management decisions can only be made after a thorough evaluation of
the environment, assessment of the resources available, the current husbandry
system, the quantity and competence of existing or obtainable labor, and a
consideration of the economic consequences that may be associated with any
contemplated changes. Once these are defined, it is possible to decide on what
additional inputs might be required and how the environment should be improved
to enhance outputs.

The failure to detect estrus and have cows remated during the first six
monthe of lactation is a common problem in dairy herds. Detection is difficult
since the expression of estrous behavior varies between cows and also between
the first postpartum and all subsequent cycles within cows. Factors such as
group size and composition, age, health status, housing and especially footing,
influence the duration and intensity of estrus. Thus, any recommendations on
when to breed can only be elucidated in general terms. There are no magic
bullets. The currently available technologies to assist with estrous detection,
cycle control, artificial insemination and embryo manipulations are all tools
to enable good managers to become more effective. They are not panaceas that
will convert poor mangers into better ones. However, close attention to the
following points could improve reproductive efficiency in many herds.

What Can We Do About Getting Animals Mated at The Right Time?

If most animals are to be successfully mated in time to maintain a 12 to
13.5 month calving interval, efficient estrous detection must be part of the
regular management routine. The amount of time attendants can devote to this is
limited so observation periods must coincide with periods when sexual activity
is highest. Three, 20 minute observation periods, occurring just before the
morning milking, sometime during late morning to early afternoon, and again
late in the evening, would be the minimum time required. Time should not be
wasted checking for estrus at feeding or when any equipment is operating since
cows will be distracted and may not interact sexually. Both free and tied cows
become more excitable and restless as they pass through estrus. Any animals
that show increased activity or a change in normal behavior should be checked
carefully for clear mucous discharge and an enlarged, reddened vulva plus other
definitive signs of estrus when first noted and again at subsequent observation
periods. Ideally, only animals that stand firmly and accept mounting by
herdmates should be inseminated. However, on slatted floors or whenever the
footing is poor, cows not in or near estrus may be reluctant to mount others.
Thus, any female that persistently attempts to mount should be considered in
estrus. If this practice is followed, it may result in the occasional animal
being inseminated when she is just coming into estrus so cows still showing
strong signs on the day following mating should be re-inseminated.

Detecting estrus and proper timing of insemination in continuously tied cows
is difficult. Placing animals who are between 50 and 100 days postpartum in a
box stall or other loafing area between milkings provides opportunity to show
sexual behavior. If these females are watched closely in the late evening,
before the morning milking, and at some time in late morning or early
afternoon, estrous detection efficiency and pregnancy rates should improve.

Estrus and ovulation are accompanied by numerous behavioral and
physiological alterations. Some of these, like standing to be mounted, are
either present or not present and can be detected readily through visual
observation. Others, such as changing hormonal concentrations, increased
mobility (restlessness), vaginal hyperemia or temperature fluctuations, require
more sophisticated measurements. Advancement in electronic sensor technology,
combined with increased use of computers on farms, creates greater opportunity
for automated detection of estrus related phenomenon. Devices to record
mounting activity, restlessness and milk temperature changes have already been
marketed commercially. Unfortunately, these are not yet totally effective in
detecting animals in estrus and produce a number of "false positive"
responses. Further improvement can be expected as the sensor and telemetry
technology improve and experience in design and operation increase. It should
eventually be possible to provide practical electronic aids that, even if not
100% effective in predicting the optimum time for insemination, reliably focus
attention on those animals who are in or near estrus. These are only aids,
however, and cannot completely replace the eyes or the intelligence of a
knowledgeable observer.

Ultimately, it may be possible to control precisely the time of ovulation so
that acceptable pregnancy rates follow fixed-time insemination. Alternately, it
might be feasible to control estrus and ovulation, leave the cow for six to
eight days and then insert an IVF derived embryo. However, until reliable,
fully automated detection arrives, or IVF transfers become practical on
commercial farms, it is essential that routine observation for estrous behavior
remains a part of the normal work schedule.

GOALS: Establish a series of challenging but achievable goals
for each of the important reproductive parameters such as heifer age at first
mating, proportion of cows detected and mated by 75 or 80 d postpartum,
pregnancy rate to first service, days open, services per pregnancy,
adjusted calving-interval, and culling for
infertility. The most common reason that dairy farmers fail to meet goals
is because they do not have any.

IDENTIFICATION: Mark all heifers and cows by a method that
allows immediate and positive recognition of each individual and her
reproductive status. The use of different colored
tapes placed around the base of the tail
or on neck straps to indicate cows ready for mating or mated but not yet
confirmed pregnant, work well in many herds

RECORDS: Maintain comprehensive records that include all
estrous dates, mating dates and any gynecological observations. Various
computer programs will summarize herd performance and highlight the current
reproductive status for individual cows. These are only worthwhile if someone
regularly enters current data and interprets the output. Remember,
anything not measured accurately cannot be managed effectively.

RESPONSIBILITY: Assign all estrous detection duties and
responsibilities to one experienced and motivated individual. This person must
have ample time for observations, record keeping and all other related
activities. Someone must be held accountable for performance and should
receive a financial bonus for meeting or exceeding reproductive goals.

COMPETENCE: The owner-manager must insure that all individuals
responsible for and involved with the detection of estrus have the necessary
knowledge, training and experience to perform the task properly.

TIME: a) Devote a minimum of one hour per day entirely towards
observing cows for estrous signs. Ideally, this should be divided into three,
20 minute periods occurring at times when the animals are not distracted by any
other activities. More time will be required in larger herds or if animals are
housed in several units.

b) An observation period late in the evening can often detect estrous
females that did not show obvious signs earlier in the day or identify those
demonstrating increased excitability associated with coming into estrus. To be
successful, this late check must be done quietly without disturbing most of the
herd. In tie stall barns look specifically for cows that are already standing
or get up immediately on sensing the attendant's presence. This alone does not
indicate estrus but serves to identify an animal that should be watched closely
for the next 24 hours. When on pasture or in free stall housing, most cows will
be lying and ruminating quietly during the evening. The observer should
investigate closely any individuals that are up and clustered closely together
since females in or near estrus form a sexually active group.

FACILITIES: a) Turn tied animals out at regular intervals for
exercise into an area providing good footing and freedom from distractions.
Provision of an exercise pen in which females at the appropriate stage for
rebreeding can spend part or all of the daytime or nighttime hours is a useful
addition in many tie-stall herds with estrous detection difficulties. Exercise
periods provide opportunity for cows to display behavioral signs but this
only contributes to detection efficiency if someone is there to see and record
mounting activity.

b) Cows in free stall or loafing units should also be observed regularly and
at times when they are not disturbed by other activities. In larger herds,
grouping of cows according to lactation stage and
management requirements is an excellent practice since this places all
animals between two and five-month postpartum together. Thus, observations for
estrous detection can be focused on those in the appropriate period when
rebreeding should take place.

DETECTION AIDS: a) Use visual reminders that provide obvious
indication which animals are due for postpartum checking, mating, pregnancy
diagnosis, special treatment or drying off. Items such as computer programs,
breeding wheels, 21 day calendars, neck or ankle straps and individual
colored tapes indicating reproductive
status are all valuable management aids when used properly, but serve no useful
purpose unless kept current and consulted daily.

b) Other estrous detection aids such as electronic sensors,
chin ball markers,
tail paint, heat mount indicators,
teaser bulls, and even estrous cycle
control procedures are available to help identification of proper time for
mating. When used properly, estrous detection aids are tools that can
assist an already competent herdsperson to do a better job. They are not
crutches that will compensate for poor husbandry.

EVALUATION: The entire reproductive management program and performance
should be evaluated at frequent intervals to insure that management goals are
being met or to initiate corrective procedures whenever these are
indicated.